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Collections are a way for you to organize kata so that you can create your own training routines. Every collection you create is public and automatically sharable with other warriors. After you have added a few kata to a collection you and others can train on the kata contained within the collection.
Get started now by creating a new collection.
[...] is called the spread syntax. When we write [...str], it spreads the string into an array of its individual characters. This is necessary because reverse() only works on arrays.
Without the spread (just [str]), you'd get an array with the entire string as a single element — not what we want in this case.
First argument — the starting index, Second argument — the ending index (not included in the result)
why is it 1 and not 0, -1?
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